The late Russian inventor of the AK-47 assault rifle wrote shortly before his death that he felt guilty about what he had created.

Mikhail Kalashnikov, who died in December at age 94, expressed his regrets last April in a letter to Patriarch Kirill, the head of the Russian Orthodox Church, BBC reports. He said the “spiritual pain is unbearable” because of the many deaths caused by the rifle.

“I keep having the same unsolved question: if my rifle took away people’s lives, then can it be that I… am guilty for people’s deaths, even if they were enemies?” Kalashnikov wrote .

The letter was published by the Russian newspaper Izvestia, BBC reports. Kirill responded to his letter, his spokesman Alexander Volkov said. “The Church has a very definite position: when weapons serve to protect the Fatherland, the Church supports both its creators and the soldiers who use it,” Volkov said.

Kalashnikov’s 1947 AK-47 design was the standard equipment of the Soviet army and has since become one of the world’s most ubiquitous and widely used weapons. Kalashnikov has expressed sadness in the past for its popularity: “It is painful for me to see when criminal elements of all kinds fire from my weapon,” he said in 2008.